Genetic studies and role in virulence of mannose-resistant/proteus-like (MR/P) fimbriae of uropathogenic Proteus mirabilis

Abstract

Proteus mirabilis, a cause of serious urinary tract infection (UTI), produces at least five types of fimbriae, among them, mannose-resistant/Proteus-like (MR/P). This fimbria binds to tubular epithelial cells in vitro, and has been implicated as a factor in the development of acute pyelonephritis. Mice challenged with P. mirabilis developed antibody response to MR/P fimbriae, indicating that these fimbriae are produced in vivo in the course of UTI. MR/P fimbriae were isolated and purified from a uropathogenic strain and were shown to have a major structural subunit with apparent molecular weight of 16.4 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The N-terminal amino acid sequence of this subunit was similar to that of SmfA and PapA, the major fimbrial subunits of uropathogenic Serratia marcescens and Escherichia coli, respectively. To study the genetics of the MR/P fimbriae, genes encoding these fimbriae were isolated from a genomic library of P. mirabilis. E. coli carrying the recombinant plasmid expressed MR/P fimbriae as detected by colony immuno-blotting using monoclonal antibody specific to MR/P fimbriae and by hemagglutination assay. The nucleotide sequence revealed that the mrp gene cluster is comprised of 7293 bp which predicts 8 polypeptides: Mrpl (22.1), MrpA (17.9), MrpB (19.6), MrpC (96.8), MrpD (27.9), MrpE (19.5), MrpF (17.4), and MrpG (13.2 kDa). mrpl is located upstream of the mrpA and is transcribed in the opposite direction of the rest of the operon. Predicted polypeptides share similarities with polypeptides encoded by pap and smf gene clusters, suggesting a similar function in the biogenesis of the MR/P fimbriae. To investigate the contribution of the MR/P fimbriae to the pathogenesis, a MR/P fimbrial mutant was constructed by allelic exchange. Virulence of mutant and parent strains was compared in an animal model of ascending UTI. CBA mice (N = 40) were challenged transurethrally with mutant or parent strain. After 1 week, geometric means of CFU/ml urine or /g bladder and kidney for parent and mutant strains, respectively, were: urine: 7.79 vs 7.02 (p = 0.035); bladder; 6.22 vs 4.78 (p = 0.019); left kidney: 5.02 vs 3.31 (p = 0.009); and right kidney: 5.28 vs 4.46 (p = 0.039). Overall, the counts for the mutant strain averaged about 15 times less than for the parent strain, suggesting that MR/P fimbriae contribute to colonization of the urinary tract.